The invention relates to a composition of matter and to a method of rotationally molding same.
In the last 25 years or so, there has been a tremendous growth in the use of plastics to produce a variety of consumer goods and industrial products. Such materials lend themselves to different production methods and techniques. Frequently the production method is dictated by the particular article to be manufactured. For example, production of large plastic articles is accomplished for the most part by rotational molding, or at least the rotational molding process finds particular applicability in the production of large hollow products. Ethylene polymers, homopolymers as well as copolymers, are used extensively in rotational molding applications. In many instances the ethylene polymers used for rotational molding are compounded with various crosslinking agents and additives which stabilize the properties of the molded polymer when exposed to heat, light, etc., as is well known in the art. However, it has been found that the presence of such additives, while solving one problem, can create another problem. One such problem that is created when solid pigments are added to the polymer along with a crosslinking agent is the formation of bubbles. The bubbles are undesirable since they can be relatively large, e.g., up to about 1/8 inch (3.2 mm) in diameter or more, can extend to each surface of the walls and can terminate in pin hole or larger openings. As a result, articles produced from this type of polymer are unsuitable for many uses. Also, the appearance and the impact strength of the molded articles can be adversely affected by a large bubble population.
An object of the invention is a composition of matter suitable for producing rotationally molded articles with a minimum formation of bubbles.
Another object of the invention is the production of rotationally molded articles from polymers with a minimum formation of bubbles.
Another object of the invention is the reduction or elmination of the bubbles formed when rotationally molding ethylene polymers containing solid pigments and crosslinking agents.